Pouring tube

ABSTRACT

The present invention concerns a pouring tube of refractory material comprised of a tubular element and equipped at its upper end with a plane plate, the side faces and lower face of the said plate and the upper end of the tubular part being protected by a metallic case, said plate being reinforced in its lower face by mechanical means that increase its stiffness that is characterized in that these stiffening means are comprised of a plurality of U-shaped metallic pieces located on either side of the tube and attached fixedly to the part of the metal case protecting the lower face of the plate. These tubes present a greater resistance to the formation of cracks than conventional tubes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a pouring tube for conveying a moltenmetal from an upper metallurgical vessel to a lower one. In particular,it concerns a pouring tube of refractory material for the transfer ofmolten steel from a distributor to an ingot mold or alternatively from apouring ladle to a distributor.

2. Description of the Prior Art

Pouring tubes designed to convey the molten metal from one metallurgicalvessel to another are wear pieces highly stressed to the point thattheir service life could limit the pouring time. Numerous devices forintroducing and changing the tube described recently in the prior artpermitted resolving this problem. See, e.g., European Patents 192019 and441927. As soon as the erosion in the vicinity of the meniscus, and evensometimes inside of the pouring tube, reaches a certain level, the worntube is replaced with a new tube within a sufficiently short time so asnot to interrupt the pouring. In these devices, a pouring tube comprisesa tubular piece equipped at its upper end with a plane plate designed toslide in guides against the lower plane face either of a pouring orificesuch as a nozzle or of a fixed bottom plate coupled to a mechanism forregulating the pouring jet inserted between the pouring orifice (e.g.,nozzle) and the pouring tube is generally used.

These tubes can be in one piece or can consist of an assembly of severalrefractory pieces. In most cases, the side faces of the plate, the lowerface of the plate and the upper end of the tubular part of the tube areprotected by a metal case.

Despite the considerable advantages imparted to the state of the art bythe systems described above and the continuous improvement that theyhave undergone in recent years, there are still some problems.

In particular, the appearance of cracks or microcracks is frequentlyobserved in the pouring tube at the level of the junction between thetubular piece and the plate located at the upper end of the tubularpiece. These cracks or microcracks can occur from the preheating of thetube prior to its use, the first moments of its use or during its use.

Even if these cracks have a negligible size in some cases, they must betaken into account. The passage of the molten metal in the tube inducesa substantial aspiration of ambient air. Atmospheric oxygen or evennitrogen are substantial sources of contamination of the molten metal,in particular, steel. In addition, under the combined action of oxygenand very high temperatures, the refractory material can be considerablydegraded at the point of arrival of oxygen, i.e., the crack. Thisdegradation further contributes to a local deterioration of therefractory material and enlarges the crack to the point that it could benecessary to stop the pouring.

There are refractory materials more resistant to cracking. However,these materials are generally sensitive to other phenomena such aserosion, corrosion, etc. Furthermore, the cracking can be caused by athermal shock, a mechanical shock or the application of excessively highmechanical stresses such as pressure or vibrations.

In particular, in a device for introducing and changing the tube, theplate undergoes substantial bending stresses perpendicular to itssurface that may be responsible for the formation of cracks at the upperend of the tubular part. It is observed that the upper plate can bedeformed by bending around an axis parallel to the direction of theguides in which the said plate slides. Thus, it is difficult to reach acompromise based only on the chemical composition of the refractorymaterial that solves all these problems. The applicant thus undertook tofind a means of reducing the formation of cracks in the pouring tubewithout having to modify the composition of the refractory material.

European patent application 601,700 discloses a pouring tube ofrefractory material comprised of a tubular element and equipped at itsupper end with a plane plate. The side faces and lower faces of the saidplate and the whole tubular part of this pouring tube are protected by ametal case. A reinforcing cone surrounds the upper end of the tubularpart.

Such a reinforcing cone stiffens homogeneously the structure all aroundthe upper end of the tubular part. However, as explained above, it hasbeen observed that, in case of use in a device for introducing andchanging a pouring tube, the pouring tube is subject to constraintswhich are not homogeneously distributed. Moreover, its large hindranceprevents the use of a cone reinforced tube such as disclosed in theEuropean patent application 601,700 in a device for introducing andchanging a pouring tube.

Other reinforcing means for refractory pouring tubes are known in theart such as for example WO 8902800 and WO 9220480, wherein the metaljacket itself is said to strengthen the tube.

SUMMARY OF THE INVENTION

The present invention thus concerns a pouring tube of refractorymaterial comprised of a tubular element and equipped at its upper endwith a plane plate, the side faces and lower face of the said plate andthe upper end of the tubular part being protected by a metallic case,said plate being reinforced in its lower face by mechanical means thatincrease its stiffness that is characterized in that these stiffeningmeans are comprised of a plurality of U-shaped metallic pieces, at leastone being arranged on each side of the tube and attached fixedly to thepart of the metal case protecting the lower face of the plate, and tothe upper end of the tubular part.

DETAILED DESCRIPTION OF THE INVENTION

Preferably, the attachment means of the U-shaped pieces comprises atleast two linear welds arranged on either sides of and in contact withthe upper end of the tubular part and parallel to the direction of theguides (sliding direction). These welds fixedly attach the ends of theU-shaped piece to the lower face of the plate and tangentially to thetubular part.

Advantageously, the gaps between the ends.of the respective U-shapedelements are filled with another weld which extends orthogonaly to theplate, forming a T-shaped weld with the linear weld attaching theU-shaped piece to the lower face of the plane plate.

In this case, it is also preferable that the U-shaped pieces permit atleast a limitation of the bending of the plate around an axis parallelto the direction of the guides in which the said plate slides. To thisend, the U-shaped pieces can be disposed so that their side branches areparallel to the direction of the guides.

The side branches of the U-shaped pieces advantageously have a lengthsuch that the ends of the two U-shaped pieces are close to each otherand can even be in mutual contact. According to this form ofimplementation, the plate is rendered more rigid in two perpendiculardirections. The U-shaped pieces are preferably arranged so that theirside branches are parallel to the direction of the guides; in thismanner, the bending of the plate around axes parallel and perpendicularto the direction of the guides in which the said plate slides islimited.

These pieces have the effect of increasing the height of the piecesubjected to bending stresses and consequently increase its bendinginertia. These pieces have a height between 1 and 20 cm, preferablybetween 2 and 8 cm.

The applicant was able to determine that the pouring tubes according tothe present invention became cracked definitely less than conventionaltubes. In the case of a pouring tube for conveying a molten metal from adistributor to an ingot mold, the lower end of the pouring tube quitefrequently has two lateral openings for the flow of molten metal intothe ingot mold. These openings located on either side of the tube shouldbe oriented in the ingot mold along an axis parallel to the largerdimension of the ingot mold. It is imperative that the pouring tubeengages correctly in the ingot mold. A wrongly oriented tube wouldinduce a flow of the molten metal toward the walls of the ingot mold andwould be responsible for substantial perturbations in solidificationzone of the metal. These perturbations can result in a laceration of theskin of the solidifying slab and thus a breakthrough of molten metalunder the ingot mold. To avoid orienting a replacement pouring tubewrongly in a device for introducing and changing a pouring tube, it wasproposed to provide the lower face of the plane plate with ananti-inversion device. This device gives the part of the plate designedto slide in the guides an asymmetric (rectangular or ellipsoidal) formso that it is impossible to engage the plate in the said guides with anunintended orientation. The U.S. Pat. No. 5,188,743, for example,describes such a system.

Advantageously, the mechanical means that increase the stiffness of theplate also serve as anti-inversion device. For this purpose, they arearranged around the tubular part of the pouring tube in an asymmetricmanner so that the tube cannot be engaged with an incorrect orientationin a device for introducing and changing the tube.

During the development of the present invention, the applicant alsofound that in some cases the very high temperatures reached by thedifferent parts of the pouring tube during the passage of the moltenmetal can cause a softening of the mechanical means reputed to increasethe rigidity of the plate and strip them of any efficacy. This problem,when it was observed, could be resolved by using pieces having aheat-dissipating structure. For example, the lower end of the saidpieces can be indented or crenellated to induce a substantial aircirculation at their level. In a variant or in combination, at least apart of these pieces can also be provided with fins in order to induce asubstantial air circulation at their level.

What is claimed is:
 1. A refractory pouring tube adapted to travel in asliding direction within a tube-changing device comprising: a) a tubularpart comprising an upper end and a plane plate upstream from the upperend, the plane plate having a plurality of side faces and at least onelower face; b) a metal case covering a portion of the upper end, thelower face and a plurality of the side faces; and c) at least twoU-shaped reinforcements, each having two arms, arranged around the tubeand fixedly secured to the metal case at the lower face and the upperend of the tubular part.
 2. The refractory pouring tube of claim 1,wherein the U-shaped reinforcements are secured to the metal case withat least two linear welds arranged on opposite sides of and in contactwith the upper end of the tubular part and parallel to the slidingdirection.
 3. The refractory pouring tube of claim 1, wherein theU-shaped reinforcements reduce the flexion of the plane plate around anaxis parallel to the sliding direction.
 4. The refractory pouring tubeof claim 1, wherein the U-shaped reinforcements are arranged around thetube such that the arms of adjacent U-shaped reinforcements areseparated by a gap.
 5. The refractory pouring tube of claim 4, whereinthe gap is filled in with a weld that extends orthogonally from thelower face of the plate.
 6. The refractory pouring tube of claim 5,wherein the U-shaped reinforcements are secured to the metal case withat least two linear welds arranged on opposite sides of and in contactwith the upper end of the tubular part and parallel to the slidingdirection, and the weld forms a T-shaped weld with the linear weldattaching the U-shaped piece to the lower face of the plane plate. 7.The refractory pouring tube of claim 1, wherein the U-shaped elementsare arranged with their arms parallel to the sliding direction.
 8. Therefractory pouring tube of claim 1, wherein the U-shaped reinforcementsare non-symmetrically arranged around the tubular part of the pouringtube so as the tube can not be incorrectly introduced in thetube-changing device.
 9. The refractory pouring tube of claim 1, whereinthe U-shaped reinforcements include a cooling structure selected fromthe group consisting of indentations, crenellations and fins.
 10. Therefractory pouring tube of claim 9, wherein the U-shaped reinforcementscomprise a lower part away from the lower face of the plane plate,and-the lower part comprises the cooling structure.
 11. A refractoryassembly comprising a tube-changing device and a pouring tube capable ofbeing inserted into and traveling in a sliding direction within thedevice, the pour tube comprising: a) a tubular part having an upper endcomprising a plane plate, the plane plate having a plurality of sidefaces and at least one lower face; b) a metal case covering a portion ofthe upper end, the lower face and a plurality of the side faces; and c)at least two U-shaped reinforcements, each having two arms, arrangedaround the tube and fixedly secured to the metal case at the lower faceand the upper end of the tubular part, wherein the U-shapedreinforcements prevent misinsertion in the tube-changing device.
 12. Therefractory assembly of claim 11, wherein the U-shaped reinforcements arenon-symmetrically arranged around the tubular part of the pouring tubeso as the tube can not be incorrectly introduced in the tube-changingdevice.
 13. The refractory assembly of claim 11, wherein the U-shapedreinforcements include a cooling structure selected from the groupconsisting of indentations, crenellations and fins.